The present invention involves a process of coating fibrous mats to produce a very smooth surface, the resultant coated mats and laminates containing the coated mats. These coated mats have many uses, but are especially useful in producing laminates such as a faced gypsum wallboard and faced foam products.
Fibrous non-woven mats containing fibers such as glass and/or synthetic organic fibers bound together with a resin binder are well known. Usually a solution of urea formaldehyde resin, usually modified with a thermoplastic polymer, or one of many other known resin binders is applied to a non-woven web of fibers and then dried and heated further to cure the urea formaldehyde resin or other resin binder to form a non-woven mat product. The nonwoven webs can be formed dry or from an aqueous dispersion. Typical processes are disclosed in U.S. Pat. Nos. 4,112,174 and 3,766,003, the disclosures of which are hereby incorporated herein by reference.
The fiberglass mat (Johns Manville's 7502 Mat (99 gms/square meter) made using a binder of modified urea formaldehyde resin performed well in the process disclosed in U.S. Pat. No. 4,647,496 to make a faced insulating gypsum board, also disclosed in that patent, but the mat was not as strong as desired which caused process breakouts adding to production costs. This mat was also more rigid than desired which made it difficult to fold around the edges of the board and also irritated the hands and arms of the workers handling and installing the insulating board product. Further, when the faced insulated gypsum board was cut, the dust from the mat was excessive and further irritated those it contacted, particularly if the workers bare arms, etc. were sweaty and exposed to the dust. Skin abrasion and irritation was also a problem for those handling the mat and the faced board when not wearing gloves and long sleeve shirts. The mat also contained “stand-up fibers” which can rub or roll off during manufacture of composite products such as gypsum panels or foam board insulation when it is conveyed or stacked which can cause problems later when the wallboard is painted.
To address the inadequate strength problem a small portion of polyester, polyethylene terephthalate (PET), fibers can be used in place of an equal amount of glass fibers and the urea formaldehyde resin binder was replaced with an acrylic binder containing a small amount of a stearylated melamine. This improved the strength adequately and also improved the handling characteristics of the mat somewhat, i. e. the mat is friendlier to those handling and installing the mat or board, but the acrylic bound mat is more expensive and less fire (flame) resistant and still leaves some glass fibers exposed. Such mats are disclosed in U.S. Pat. No. 5,772,846. While the mats disclosed by this latter reference have substantially improved “hand” and cause very little abrasion or discomfort in handling, the cost is higher, the mat is less flame resistant than the mat disclosed in U.S. Pat. No. 4,647,496 and further improvement is still desired by some users.
A great amount of work has been done to try to eliminate the “stand up fiber” problem including coating the nonwoven fiberglass mats. U.S. Pat. No. 5,112,678 discloses coating compositions aimed at solving this problem containing inorganic compounds such as limestone, clay, quicklime, etc. and up to 5 percent of a polymer binder, but the coating weight was very high at 15-120 pounds per thousand square feet and this coating did not provide all the results desired for some applications such as a facer for gypsum board. This patent does not disclose the method of coating, but instead states “the coating was applied with a coater especially designed for porous glass mats”, but does not disclose what the special design was. It does disclose that the coating mixture penetrated entirely through the thickness of the mat which suggests that the compositions disclosed are not exactly coatings, but rather are impregnating compositions that can end up thicker than the mat substrate.
Published U.S. patent application No. 20030134079 discloses a coated fibrous mat for gypsum wallboard reportedly having improved strength versus uncoated mat by controlling the depth of penetration of the coating, but the need for a smoother surface is not addressed.
U.S. Pat. Nos. 5,397,631 and 5,552,187 discloses coating a fiberglass mats after the mats are laminated to a gypsum board. The coating compositions comprise 15-35 percent of a resin binder and 20-65 percent filler comprising inorganic compounds that include limestone and calcined clay. The coating composition is applied to the glass mat with some kind of a roller the coated mat attached to the rigid board is then dried in an infra-red oven to produce a heavy coating weight of 50-100 pounds per thousand square feet. Such coatings have a substantially rougher exposed surface than does the kraft paper facer normally used on gypsum board and this is undesirable.
There still exists a need for nonwoven fiberglass mats that has better flame resistance, lower cost, a smoother surface, good handlability (flexible and non abrasive/non irritating to the skin) and none or far fewer “stand-up fibers”. Such are provided in the present invention.